Below grade cask transfer facility

ABSTRACT

A system and method for transferring a canister of spent nuclear fuel from a transfer cask to a receiving cask. In one aspect, the system comprises a below grade opening adapted for receiving a cask; a platform positioned within the opening, the platform capable of vertical movement; and at least two jacks for vertically moving the platform; wherein the platform is capable of lowering the cask within the opening.

BACKGROUND OF THE INVENTION

This invention relates to the field of storing and transferring spentnuclear fuel and specifically to a method and system for transferringspent nuclear fuel from a transfer cask to a receiving cask.

In the operation of nuclear reactors, it is customary to remove fuelassemblies after their energy has been depleted down to a predeterminedlevel. Upon removal, this spent nuclear fuel is still highly radioactiveand produces considerable heat, requiring that great care be taken inits packaging, transporting, and storing. In order to protect theenvironment from radiation exposure, spent nuclear fuel is first placedin a canister. The loaded canister is then transported and stored inlarge cylindrical containers called casks. A transfer cask is used totransport spent nuclear fuel from location to location while a storagecask is used to store spent nuclear fuel for a determined period oftime.

In a typical nuclear power plant, spent nuclear fuel is loaded into acanister while submerged in a pool of water. The canister is sealed andloaded into a transfer cask while still submerged in the pool. Onceloaded with the canister, the transfer cask is used to transport thecanister to a receiving cask (i.e., a storage cask or a transport cask).The loaded canister is then transferred from the transfer cask to thereceiving cask for either storage or further transport. During transferfrom the transfer cask to the receiving cask, it is imperative that theloaded canister is not exposed to the environment.

As a result of this need, the prior method for transferring a loadedcanister from a transfer cask to a receiving cask is to raise thetransfer cask above the receiving cask and secure the transfer cask atopthe receiving cask so that the casks are in a vertically stackedorientation. The transfer cask is adapted so that its bottom can beopened while it remains stacked upon an open receiving cask. Once thebottom of the transfer cask is opened, the loaded canister is loweredfrom the transfer cask into the receiving cask with a negligible amountof radiation exposure to operations personnel.

Most casks are very large structures and can weigh up to 250,000 lbs.and have a height of 16 ft. or more. As such, stacking a transfer caskatop a receiving cask requires a lot of space a large overhead crane andpossibly a restraint system for stabilization. Typically, the transferof a loaded canister using this stacking method is done inside a 10C.F.R. 50 structure of a nuclear power plant, which is fully equippedwith an overhead crane and radiation containment devices to protect thehealth and safety of the surrounding communities in the event of aloading mishap. However, numerous nuclear power plants do not possess a10 C.F.R. 50 qualified staging area that is either large enough toaccommodate the stacking of the transfer cask and receiving cask,qualified to support the load of the stacked casks, and/or possessesqualified load handling equipment to make the canister transfer indoors.For such sites, the canister transfer must be completed outdoors usingsystems and devices that provide the same or greater level ofoperational safeguards that are available inside a nuclear power plantstructure that is fully certifiable for indoor transfer.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method and systemfor transferring a loaded canister of spent nuclear fuel from a transfercask to a receiving cask that requires less vertical space.

Another object of the present invention is to provide a method andsystem for outdoor transfer of a loaded canister of spent nuclear fuelfrom a transfer cask to a receiving cask outdoors that provides the sameor greater level of operational safeguards that are available inside afully certified nuclear power plant structure.

Yet another object of the present invention is to provide a method andsystem for ergonomically completing cask operations necessary fortransferring a loaded canister of spent nuclear fuel from a transfercask to a receiving cask.

Still another object of the present invention is to provide a method andsystem that greatly enhances the radiation shielding during the transferof a spent nuclear fuel from a transfer cask to a receiving cask.

Another object of the present invention is to provide a method andsystem that eliminates personnel lifts and scaffolding that is needed tocomplete transfer of spent nuclear fuel from a transfer cask stackedatop a receiving cask to the receiving cask.

These objects and others are met by the present invention which in oneaspect is a system for transferring spent nuclear fuel to a caskcomprising a below grade opening adapted for receiving a cask; a casksupport means positioned within the opening, the cask support meanscapable of vertical movement; and means for vertically moving the casksupport means; wherein the cask support means is capable of lowering thecask within the opening.

Preferably, the system further comprises a shell having a cross section,the shell forming walls of the opening wherein the cross section of theshell is slightly larger than the cross section of the cask. The shelland the cask are usually cylindrical.

Also preferably, the means for vertically moving the cask support meansis at least two lifting jacks. Moreover, the at least two jacks can becoupled so as to keep the cask support means approximately level duringvertical movement. In the preferred embodiment of the system, the numberof lifting jacks is three and are located outside the opening andaccessible from grade level.

The cask support means has a fully lowered position and a fully raisedposition. Preferably, when the cask support means is in the fully raisedposition, the cask support means is below grade. Also preferably, whenthe cask support means is in the fully lowered position and supporting acask having a height, at least a major portion of the cask's height isbelow grade, with approximately 30 inches of the cask above grade whenthe cask support means is in the fully lowered position and supporting acask.

The opening can have a bottom, and the system can further comprise asetdown structure positioned at the bottom of the opening and below thecask support means. In such an embodiment, when the cask support meansis in a fully lowered position, the cask support means contacts thesetdown structure and the cask support means, and any load being borneby the cask support means is supported by the setdown structure.Preferably, the cask support means is a platform having a center and atop surface wherein the cask support means has a hole near the centerand a plurality of cask positioning plates on the top surface.

The system can further include vertical guide rods on which the casksupport means can move. Preferably, the vertical guide rods have a topand a bottom, the vertical guide rods being secured at the top so thatupon loading the cask support means, the vertical guide rods are intension.

In another aspect, the invention is a method of transferring a canisterof spent nuclear fuel to a cask comprising the steps of: lowering areceiving cask having a height into a below grade opening so that aportion of the receiving cask's height is below grade level; andtransferring the canister to the receiving cask.

The preferred method further comprises placing the receiving cask on acask support means located within the opening, the cask support meanscapable of vertical movement; lowering the receiving cask into theopening by lowering the cask support means; aligning the canister abovethe receiving cask; and lowering the canister into the receiving cask.

Preferably, jacks are used to lower the cask support means wherein thelifting jacks can be coupled so as to keep the cask support meansapproximately level during vertical movement. The preferred number oflifting jacks is three and the jacks are preferably outside the openingand are accessible from grade level.

Also preferably, a shell having a cross section can be used to formwalls of the opening. The shell and the receiving cask can becylindrical. The cross section of the shell is preferably slightlylarger than the cross section of the cask. Also preferably one or morelateral restraints are inserted between the shell and receiving cask.

Preferably, the cask support means has a fully lowered position and afully raised position, wherein when the cask support means is in thefully raised position the cask support means is below grade level. Alsopreferably, when the cask support means is in the fully loweredposition, at least a major portion of the cask's height is below gradelevel. When the cask support means is in the fully lowered position, itis preferable that about 30 inches of the cask be above grade level.

The opening preferably has a bottom with a setdown structure positionedat the bottom of the opening and below the cask support means. It ispreferable that when the cask support means is in a fully loweredposition, the cask support means contacts the setdown structure, thecask support means and any load being borne by the cask support meansbeing supported by the setdown structure.

Preferably, the cask support means is a platform having a center and atop surface wherein the cask support means has a hole near the centerand a plurality of cask positioning plates positioned on the topsurface. Also preferably, the cask support means moves along a pluralityof vertical guide rods. It is preferred that the vertical guide rodshave a top and a bottom, the vertical guide being secured at the top sothat any loading from the cask support means results in the verticalguide rods being in tension.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view partially in section of the system of thepresent invention, a below grade cask transfer facility.

FIG. 2 is a perspective view partially in section of the cask transferfacility wherein a circular platform is in a fully raised position andsupporting a loaded receiving cask partially in section.

FIG. 3 is a perspective view partially in section of the cask transferfacility wherein the circular platform is in a fully lowered positionand supporting a loaded receiving cask partially in section.

FIG. 4 is a side elevational view of a receiving cask with a lid andfully lowered into the cask transfer facility.

FIG. 5 is a side elevational view of a receiving cask with its lidremoved and fully lowered into the cask transfer facility.

FIG. 6 is a side elevational view of a receiving cask fully lowered intothe cask transfer facility with a mating device secured to its topsurface.

FIG. 7 is a perspective partially in section of a transfer cask holdinga canister of spent nuclear fuel placed atop a below grade receivingcask.

FIG. 8 is a perspective view partially in section of a transfer caskplaced atop a below grade receiving cast wherein the canister of spentnuclear fuel has been lowered into the receiving cask.

FIG. 9 is a perspective view of a cask transporter used in connectionwith the system of the present invention.

DETAILED DESCRIPTION

FIG. 1 illustrates an embodiment of the system of the present invention,a below grade cask transfer facility (“CTF”) 2. As used herein, the term“below grade” means elevationally below ground surface level 6.Generally, CTF 2 comprises below grade opening 3, circular platform, andat least two jacks 5. In the illustrated embodiment, there are threehigh-capacity jacks 5 (only two are visible in the illustration). Whilejacks 5 are used to vertically move circular platform 4, circularplatform 4 can be vertically moved by any type of pneumatic ormechanical lifting device capable of lifting the applied load.

Referring to FIG. 2, CTF 2 is constructed so that receiving cask 9having lid 22, top surface 12 (FIG. 5) and base 13 can be placed on andsupported by platform 4. Receiving cask 9 can be a storage cask or atransport cask. Receiving cask 9 is placed on platform 4 when platform 4is in a fully raised position. When platform 4 is in the fully raisedposition, top surface 8 (FIG. 1) of platform 4 is below grade. Whenreceiving cask 9 is placed thereon, base 13 of receiving cask 9 is alsobelow grade, preferably about 40 inches. Platform 4 is capable ofvertical movement, including lowering receiving cask 9 into opening 3.

Referring to FIGS. 3 and 4, platform 4 can be lowered to a fully loweredposition while supporting receiving cask 9. CTF 2 is designed so thatwhen platform 4 is supporting receiving cask 9 and in the fully loweredposition, receiving cask 9 is in a position wherein a majority of itsheight is below grade. Preferably, all of receiving cask 9 will be belowgrade except about 30 inches. When all but about 30 inches of receivingcask 9 is below grade, top surface 12 (FIG. 5) of receiving cask 9 is atan ergonomic height to facilitate cask operations.

Referring to FIGS. 1 and 2, in the illustrated embodiment, CTF 2 furthercomprises a shell 15 that forms the walls of opening 3. In constructingCTF 2, shell 15 is placed in an oversized hole in the ground 6 andleveled approximately flush with the ground surface 6. The areasurrounding shell 15 can be backfilled with soil and/or concrete tosecure shell 15 in the ground 6 and to provide extra radiationshielding. As such, shell 15 establishes the inner form for a concretepour. The bottom of shell 15 may be open-bottomed to allow the insidebottom to be filled with concrete and leveled or equipped with setdownstructure 16. In the illustrated embodiment, shell 15, opening 3, andreceiving cask 9 are cylindrical. However, shell 15, opening 3, andreceiving cask 9 can be made to be any shape or size.

Preferably, shell 15 has a cross-section that is shaped and sized sothat there is a tight clearance between shell 15 and receiving cask 9when receiving cask 9 is resting on platform 4. Having a tight clearancebetween shell 15 and receiving cask 9 provides a safeguard againstreceiving cask 9 tipping over during a seismic event. When there is atight clearance between shell 15 and receiving cask 9, receiving cask 9can not tip over during a seismic event when receiving cask 9 is restingon platform 4 in the fully lowered position. When receiving cask 9 isresting on platform 4 in the fully raised position, base 13 of receivingcask 9 is below grade. Thus, a portion of receiving cask 9 forms a tightclearance with shell 15, providing seismic stabilization and decreasingthe chance that receiving cask 9 will tip over during a seismic event.

Additionally, shell 15 is designed to have a plurality of extensionspaces 17 for mounting jacks 5. Extension spaces 17 provide spaceoutside the main circumference of shell 15 so that jacks 5 do notcontact or interfere with receiving cask 9 when it is lowered. Becausejacks 5 are mounted to shell 15, shell 15 provides the support for jacks5 during lifting and lowering of platform 4 (and any applied load).Shell 15 also provides lateral support of platform 4 during operations.

While in the illustrated embodiment, shell 15 is used to form the wallsof opening 3, CTF 2 can be constructed without employing shell 15. Insuch a situation, opening 3 is formed by digging a hole in ground 6 thatapproximates the desired size of opening 3.

In FIG. 1, platform 4 is a circular platform having hole 7. Hole 7provides personnel access to the underside of the circular platform.Alternatively, platform 4 can be a frame or other structure capable ofsupporting receiving cask 9 containing loaded canister 11. Asillustrated, platform 4 has top surface 8 with cask positioning plates14 located thereon. Cask positioning plates 14 act as key ways to helpcenter receiving cask 9 on platform 4 and within opening 3.

Platform 4 is designed to approximate the shape and size of receivingcask 9, with projections 16. Platform 4 is a rugged steel weldment thatprovides support for receiving cask 9 and transmits lateral loads toshell 15 during seismic events. Platform 4 also transmits the liftingand controlled lowering forces supplied by jacks 5 to receiving cask 9.This is accomplished by projections 16 that form lifting locations forjacks 5. Projections 16 ride inside extension spaces 17.

Jacks 5 are located just outside the main diameter of the shell 15 inextension spaces 17. Jacks 5 are supported at their top end in extensionspaces 17. Jacks 5 comprise guide rods 25 that guide the movement ofplatform 4. Because jacks 5 are connected to shell 15 only at their top,vertical guide rods 25 are in constant tension under loading conditions,which eliminates the danger of “buckling.” When jacks 5 lower platform 4and any load supported thereby to the fully lowered position, platform 4contacts and rests on setdown structure 16. At this position, setdownstructure 16 bears the entire load of platform 4 (and any load supportedthereby), freeing jacks 5 and vertical guide rods 25 from supporting theapplied load (FIG. 3).

Jacks 5 are coupled mechanically or electronically to keep platform 4level during lifting operations. Jacks 5 provide sufficient lift forceto raise the platform 4 when loaded with receiving cask 9 and areoverrated to provide an extra safety margin. Jacks 5 contact theunderside of projections 16 of platform 4 in extension spaces 17. Allparts of jacks 5 and their drives 18 are located below grade to preventinterference with delivery of transfer cask. Jacks 5 and their drives 18are situated in shallow steel or concrete-lined trenches and coveredwith removable, recessed covers 19.

Drives 18 and their control system provide the power and control forjacks 5. An electronic feedback system monitors the position of eachjack 5 to maintain synchronous movement of platform 4. Redundantposition switches (not illustrated) limit the travel beyond establishedpoints (independent of the drive and control system). Level monitoringswitches independently monitor the platform level and shut off jackdrives 18 if an out-of-level condition is detected. The control stationis located near CTF 2 but is sufficiently far away for the operator tooversee the movement operations. Power and control wires going from thecontrol station to drives 18 are located underground to preventinterference and damage during cask operations.

CTF 2 is used to facilitate the transfer of a canister of spent nuclearfuel from a transfer cask to a receiving cask in a more safe, efficient,and cost effective manner.

Referring to FIGS. 1 and 2, in utilizing CTF 2 for the transfer, emptyreceiving cask 9 is placed on platform 4 when platform 4 is in the fullyraised position. As receiving cask 9 is placed on platform 4, caskpositioning plates 14, located on the top surface 8 of platform 4, actas key ways to help center receiving cask 9 in CTF 2.

Referring to FIGS. 3 and 4, platform 4 (with receiving cask 9 positionedthereon) is then lowered to a fully lowered position, leaving topsurface 12 (FIG. 5) of receiving cask 9 approximately 30 inches aboveground surface level 6. A set of lateral restraints 20 can then beinstalled between receiving cask 9 and shell 15 for sites that are proneto severe earthquakes. Lateral restraints 20 act like hard bumpers tolimit the radial movement of receiving cask 9 during a seismic event.

Referring to FIGS. 5 and 6, lid 22 (FIG. 4) of receiving cask 9 is thenremoved. In the illustrated embodiment, mating device 21 is thenattached to top surface 12 of receiving cask 9. Mating device 21provides the connection between transfer cask 10 and receiving cask 9.While in the illustrated embodiment, mating device 21 is used to providea connection between transfer cask 10 and receiving cask 9 (FIG. 7), itis possible to connect transfer cask 10 directly to receiving cask 9.The method of connection is dictated by the specific designs of thetransfer cask and receiving cask used and does not affect the scope ofthe present invention.

Referring to FIG. 7, in the illustrated embodiment, transfer cask 10,containing a loaded and sealed canister 11, is then raised, placed into,and rigidly secured to mating device 21. Base 23 (shown partially insection) of transfer cask 10 is removed using mating device 21, leavingan unobstructed pathway for canister 11 to be lowered into receivingcask 9.

Referring to FIG. 8, canister 11, using slings 24 attached to topsurface 27 of canister 11, is then fully lowered into receiving cask 9until canister 11 contacts bottom 26 of receiving cask 9. Slings 24 aredisconnected and empty transfer cask 10 and mating device 21 are removed(not illustrated).

Lid 22 is then placed back on and secured to receiving cask 9. Receivingcask 9 is then raised by platform 4 of CTF 2 to the fully raisedposition. Receiving cask 9 is then lifted and removed from CTF 2 by casktransporter 28 (FIG. 9) or some other lifting device such as a crane.

The loading operations for transferring a loaded canister from atransfer cask to a receiving cask summarized above aid in understandingthe operations of CTF 2. Actual operations and cask-specific equipmentat a particular nuclear site may vary from those described herein.

The foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. As will be understood by thoseskilled in this art, the invention may be embodied in other specificforms without departing from the spirit or essential characteristicsthereof. Accordingly, the disclosure of the present invention isintended to be illustrative, but not limiting, of the scope of theinvention, which is set forth in the following claims.

What is claimed is:
 1. A system for transferring spent nuclear fuelcomprising: a cask having a horizontal cross-section for receiving thespent nuclear fuel; a below grade opening adapted for receiving thecask; a cask support means positioned within the opening, the casksupport means capable of vertical movement; means for vertically movingthe cask support means; wherein the cask support moans is capable oflowering the cask within the opening; and a shell forming walls of theopening, the shell having a horizontal cross section that is slightlylarger than the horizontal cross section of the cask.
 2. The system ofclaim 1 wherein the shell and the cask are cylindrical.
 3. The system ofclaim 1 wherein the means for vertically moving the cask support, meansis at least two lifting jacks.
 4. The system of claim 3 wherein theplurality of lifting jacks are coupled so as to keep the cask supportmeans approximately level during vertical movement.
 5. The system ofclaim 3 wherein the number of lifting jacks is three.
 6. The system ofclaim 3 wherein the jacks are located outside the opening and areaccessible from grade level.
 7. The system of claim 1 wherein the casksupport means has a fully lowered position and a fully raised position.8. The system of claim 7 wherein when the cask support means is in thefully raised position the cask support means is below grade.
 9. Thesystem of claim 7 wherein when the cask support means is in the fullylowered position and supporting a cask having a height, at least a majorportion of the cask's height is below grade level.
 10. The system ofclaim 1 wherein the opening has a bottom, the system further comprisinga setdown structure positioned at the bottom of the opening and belowthe cask support means.
 11. The system of claim 1 wherein the casksupport means is a platform having a center and a top surface.
 12. Thesystem of claim 1 further including vertical guide rods on which thecask support means can move.
 13. The system of claim 1 wherein when thecask is positioned in the opening, the horizontal cross section of theshell is substantially concentric with the horizontal cross section ofthe cask.
 14. The system of claim 1 wherein when the cask is positionedin the opening, a tight clearance is formed between the shell and thecask.
 15. A system for transferring spent nuclear fuel comprising: abelow grade opening for receiving a cask; a cask support meanspositioned within the opening, the cask support means capable ofvertical movement between a fully lowered position and fully raisedposition; means for vertically moving the cask support means; the casksupport means capable of lowering the cask within the opening whereinwhen the cask support means is in the fully lowered position andsupporting the cask, approximately 30 inches of the cask is above gradelevel.
 16. A system for transferring spent nuclear fuel a below gradeopening having a bottom and adapted for receiving a cask; a cask supportmeans positioned within the opening, the cask support means capable ofvertical movements; means for vertically moving the cask support means;the cask support means capable of lowering the cask within the opening;a setdown structure positioned at the bottom of the opening and belowthe cask support means; and wherein when the cask support means is in afully lowered position, the cask support means contacts the setdownstructure and the cask support means and any load being borne by thecask support means is supported by the setdown structure.
 17. A systemfor transferring spent nuclear fuel comprising: a below grade openingadapted for receiving a cask; a platform for supporting the cask, theplatform positioned within the opening and capable of vertical movement;means for vertically moving the platform; the platform capable oflowering the cask within the opening; the platform having a center, atop surface a hole near the center, and a plurality of cask positioningplates on the top surface.
 18. A system for transferring spent nuclearfuel a below grade opening for receiving a cask; a cask support meanspositioned within the opening, the cask support means capable ofvertical movement; and means for vertically moving the cask supportmeans; vertical guide rods on which the cask support means can move; andwherein the vertical guide rods have a top and a bottom, the verticalguide rods being secured at the top so that upon loading the casksupport means the vertical guide rods are in tension.
 19. A system fortransferring spent nuclear fuel comprising: a cask for receiving thespent nuclear fuel; a below grade opening adapted for receiving thecask; a cask support means positioned within the opening, the casksupport means capable of vertical movement between a fully loweredposition end fully raised position; means for vertically moving the casksupport means; the cask support means capable of lowering the caskwithin the opening; wherein when the cask support means is in the fullylowered position and supporting the cask, a portion of the cask is abovegrade level.